A way to extend the SIF extraction bandwidth for application of crop phenotyping: Considering canopy structure and illumination effects

Abstract

Solar-induced chlorophyll fluorescence (SIF) from hyperspectral imaging is strongly associated with agricultural indices, particularly leaf chlorophyll content (LCC), in crop phenotyping. However, confounding factors such as spectral resolution (SR), canopy structure, and illumination reduce SIF sensitivity and complicate its association with these indices. This study focused on examining the effect of SR and mitigating the influence of canopy structure and illumination to enhance SIF accuracy. This study employed theoretical simulations, experimental validation, and two field experiments comparing devices with varying SRs to extract SIF at 687 nm and 761 nm (SIFRₑd and SIFNIR). Initially, SCOPE model was used to simulate radiance trends across different SRs. Secondly, narrow-band imager with 7 nm full width at half maximum (FWHM) were then compared with radiance from sub-nanometer and ASD spectrometers (0.3 nm and 3 nm FWHM). Finally, to modify SIF measurements, canopy structure was quantified using fluorescence escape fraction (fₑₛc), while absorbed photosynthetically active radiation (APAR) and intensity component from hue-saturation-intensity color model (IHSI) were used to account for illumination. And driver factor for SIF extraction was explored. Results showed a strong relationship (R² ≥ 0.95) between original simulated radiance from sub-nanometer spectrometers and radiance resampled to 3, 5, and 7 nm FWHM. SIFNIR from the narrow-band imager correlated with the other spectrometers (R ≥ 0.64). While lower SR reduced SIF sensitivity, the narrow-band imager still showed potential for estimating LCC. Modified SIFNIR by fₑₛc, APAR, and IHSI, improved correlations with LCC (R = 0.77, 0.74, and 0.86) compared to unmodified SIFNIR (R = 0.65). Estimation model based on SIF modified by fₑₛc, APAR and IHSI presented RP² of 0.73, 0.75, 0.84 and outperformed SIF (RP² = 0.52), and photosynthetically active radiation and APAR showed R of 0.52 and 0.72 with SIFNIR, which indicated that disentangling confounding factors could enhance the sensitivity of SIF and structural effect governed SIF strongly than illumination effect. This study demonstrated the feasibility of narrow-band imagers for capturing spatial–temporal SIF variability by addressing confounding factors and can provide guidance for narrow-band instrument development for SIF extraction.

Plant phenotyping relevance

植物表現型測定のためのSIF抽出法を、スペクトル分解能・群落構造・照明の影響を考慮して開発・検証しており、LCC推定という植物形質への適用も中心的である。

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